Bear in mind I have no numbers or other reference to back up any of my claims.
Having an alliance, or stronger bond, thru marriage might not be common today, but I believe it was earlier, hence it could apply the setting of this manhua. Looking a history there were cases of a "royal duty" to enter into a marriage (without (initial) love). This applies to royalty, nobility, wealthy merchants and the like, generally its people/families in power who wish to stay as such. I think this could be called an arranged marriage, which is that grand elder suggested to elder Li.
Freedom of marriage may not be a reality for all. Certain cultures seem to prefer (parental) matchmaking - some with a freedom choice like I think the japanese omiai means.